Durig the 1840s Germany is the cradle of many radical groups, though the repressive political conditions mean that the activists tend to live elsewhere - in Brussels, Paris or London.

By far the most influential in the long run are two young men who become friends in Paris in 1844. Karl Marx is twenty-six at the time, Friedrich Engels two years younger. Their friendship is to be life-long, with the impoverished Marx frequently saved from near starvation by the generosity of Engels. They are also ideally suited as fellow warriors in the class struggle which they consider to be the central theme of politics and history.

Marx is the theorist, who has come to his political views through philosophy. As a student in Berlin he has been influenced by the dialectic of Hegel (the presiding genius of the Berlin philosophy school and only recently dead, in 1831). Hegel's theory is that progress is made towards the truth, in any context, through a process of struggle; a thesis is opposed by an antithesis, and out of the clash comes a new development, the synthesis.

For Marx this chimes well with his view of politics as class warfare. From the struggle between the bourgeoisie (the existing thesis) and the oppressed working class (the antithesis) will come a new political order (the synthesis, in the form of the triumphant working class).

But Marx knows virtually nothing of the industrial working class except what he reads. Engels, by contrast, shares an interest in Hegel but also knows factory life in all its contemporary horror. He comes from a rich German textile family. In 1842 he is sent to manage the Engels and Ermen cotton-spinning factory in Manchester. The result, after two years of acute observation and detailed research, is a highly influential sociological survey, The Condition of the Working Class in England, published in Leipzig in 1845.

So Engels can add flesh to the bones of historical materialism (also known as economic determinism) which becomes the all-embracing Marxist theory of economics, politics and history.

Marx and Engels argue that development in human society is driven not by people's will or by any cultural, legal or political achievement, but by a single economic factor - the inexorable advance in the technology of production.

In the Marxist theory of history, changes in methods of production lie behind mankind's progression through certain predictable stages. In the recent past there has been feudalism, which has now given way to the 19th-century triumph of the bourgeoisie. In the future there is the imminent Dictatorship of the Proletariat, after which an interim period of Socialism will give way to the final achievement of Communism.

This progression is not, as liberals would wish, a gradual evolution. It is a series of violent upheavals in the struggle between the classes. One such occasion has been seen in France, where the bourgeoisie has overthrown the remains of feudalism in the revolution of 1789.

Once the new production methods of the Industrial Revolution have reached a critical point, crowding together a sufficient number of exploited workers in slum conditions in the cities, the stage will be set for the next revolution. The proletariat (a word used by Marx for the industrial working class) will smash the bourgeoisie and will appropriate their accumulated wealth for the common cause.

In the subsequent Dictatorship of the Proletariat all other considerations will be subordinated to safeguarding the revolution. This stage ends once everybody is a member of the proletariat. With only one class left, the class war is over. The next and penultimate stage is Socialism.

In the classless society of Socialism it is anticipated that mankind will live in harmony (class exploitation being the root of all evil). Now it will be possible for the apparatus of state gradually to wither away. The final Marxist paradise of Communism will operate on a simple and just distribution of work and wealth - in Marx's words, 'from each according to his abilities, to each according to his needs'.

The Communist Manifesto: 1848

The basic tenets of Marxism, formulated by Marx and Engels from 1844, are presented to the world in 1848 in what is probably the most stark and powerfully written political pamphlet in history - the Communist Manifesto.

In June 1847, at a congress in London convened by a German radical group calling themselves the League of the Just, Engels persuades the delegates that they need a new name and new statutes. The chosen name is the Communist League, and the new statutes turn out to be much more uncompromising than anything heard from utopian communists such as Owen or Fourier.

In their opening statement the statutes of the Communist League boldly declare: 'The aim of the League is the downfall of the bourgeoisie and the ascendancy of the proletariat, the abolition of the old society based on class conflicts and the foundation of a new society without classes and without private property.' Soon a pamphlet is on sale in Drury Lane, aimed at German workers in London and headed with a new slogan: 'Workers of the world, unite!'

The League decides that a full manifesto of its aims is needed. The task is entrusted to Marx and Engels. They work on the document in December and January and it is printed in Paris in February 1848.

The timing could not be more fortuitous. Europe's most active year of revolutions is just beginning. The ruling classes everywhere are profoundly alarmed by the sudden and violent turn of events. Any among them who happen to read the Communist Manifesto can only have their worst fears confirmed by what is undoubtedly, from their point of view, a terrifying document. It is also one which is written with extraordinary brilliance and verve.

The manifesto begins with a now famous sentence: 'A spectre is haunting Europe - the spectre of communism.' There follows a clear account of historical materialism and of the class struggle, ending with a concise conclusion which must leap off the page for any bourgeois reader.

'The theory of the communists may be summed up in the single phrase: abolition of private property.' This stark statement is followed by two pages analysing the various objections made to such a programme. They all derive, the authors argue, not from any concept of justice but from self-interest. Again, there is a blunt summing up. 'You reproach us with intending to do away with your property. Precisely so; that is just what we intend.'

The document is uncompromisingly bleak when it describes the proposed future. All wealth and control will be in the hands of the state, with power to direct everyone's labour through the 'establishment of industrial armies' for all kinds of work including agriculture.

There follows a review of other socialist movements, all of which are dismissed as unscientific for going against the tide of historical materialism. The followers of Owen and Fourier in particular are dismissed as reactionaries, attempting to create 'social utopias ... duodecimo editions of the New Jerusalem'.

The authors rise to a superb clarion call at the end, with a deliberate echo of Rousseau: 'Let the ruling classes tremble at a communistic revolution. The proletarians have nothing to lose but their chains. They have a world to win. Workers of the world, unite!'

A large proportion of Marxist theory is already present in this brief and easily comprehensible document. It provides, as its authors intend, a practical blueprint for revolution - but also, in its endorsement of rigorous state control, an easy justification for totalitarianism.

Marx joins with gusto in the revolutionary ferment of 1848, returning to Germany to edit a radical newspaper. But when the tide of reaction turns, in 1849, he is expelled. He settles now in tolerant London, where he spends the rest of his life researching and writing. His only subsequent involvement in practical politics is his role in the International from 1864.

Das Kapital and the International: 1864-1872

Marx's reputation as the leading theorist of communism continues to grow during his years in London, as he develops and expands on the ideas already sketched in the the Communist Manifesto.

Zur Kritik des politischen Ökonomie (Critique of Political Economy, 1859), a short work dealing with goods and money, is a first instalment of the material ready to be sent to Hamburg for publication in 1867 as Das Kapital ('Capital'). (This, in turn, is announced merely as volume 1 of a larger work; volumes 2 and 3 of Das Kapital are edited by Engels from Marx's notes, after his death, for publication in 1885 and 1894.)

In 1864 a gathering of workers' organizations assembles in London. Though he has nothing to do with planning the event, Marx is naturally invited to attend. The meeting resolves to establish an International Workingmen's Association. Marx is one of fifty-five people elected to form a general council, and he rapidly emerges as the association's leader.

The First International, as it later becomes known, is the first centralized body attempting to guide and control the struggle to emancipate the working class. It aquires an increasing number of branches in the industrial cities of Europe, and busies itself with co-ordinating the political activities of its members.

Strikes are its main weapon. Advice and organisational assistance is sent to strikers; successful measures are taken to prevent employers bringing in strike-breakers from other countries; sometimes the mere news that the International is taking an active interest in a particular strike can influence an employer to come to an agreement with his workers.

The affairs of the International are conducted through weekly meetings of the general council in London, but the supreme body is a congress held annually in one of the few European cities where free speech prevails.

The first congresses are held in Geneva (1866), Lausanne (1867), Brussels (1868) and Basel (1869). There is then a gap, caused by the Franco-Prussian war of 1870-1.

The sequel to this war, the Paris commune, causes difficulties for the International. It is clearly an example of communism in action, yet it is also an isolated event which fulfils none of Marx's necessary conditions for a successul proletarian revolution. The International sends an address to the Paris workers, drafted by Marx, urging them not to undertake revolutionary action.

In the event some members of the Paris section of the International serve in the commune as individuals. But even without this link, Europe's rulers are bound to associate this extremist left-wing event with the most famous of left-wing organizations.

In 1871 Bismarck attempts to persuade all the European powers to follow the example of Germany, where mere membership of the International is high treason. The scheme founders when the British government refuses to ban the weekly meetings of its general council or to expel the foreign members, including Marx, who are living in London.

But the International by now has its own internal problems, in the proliferation of mutually hostile sects - a development which often cripples radical organizations. The most bitter split is between Marx himself and Mikhail Bakunin, a Russian revolutionary whose aim is to achieve world-wide anarchy. Bakunin (who with some prescience argues that Marxism will lead to 'official democracy and red bureaucracy') attempts to take over the International by forming a secret anarchist cell within it.

At the congress in the Hague in 1872 the International splits into two camps, the followers of Marx and of Bakunin. Both halves continue independently for some years. But this first agency of international socialism has now lost its authority.

National parties and the Second International: 1875-89

In the years following the split of the First International, socialists everywhere in Europe concentrate their energies on national political parties. The first initiatives come from the most radical nationality, the Germans. A Social Democratic Party is founded in Germany in 1875, though its activities are severely curtailed by an Anti-Socialist Law introduced by Bismarck in 1878. German immigrants to the United States are the driving force of the Socialist Labor Party established there in 1877.

By 1880 there are political parties in the Netherlands, Denmark, France and Spain all of which have the words 'social' or 'labour' in their titles.

By 1889 these parties have been joined by others in Britain, Belgium, Norway, Switzerland, Austria and Sweden. In that year the national parties convene a congress in Paris, where they resolve to establish a Second International. Unlike the first, it claims no direct authority over its members. However its deliberations, in congresses held every three or four years, are accepted as the highest public forum of the socialist movement.

The majority of the national parties at this stage are broadly Marxist in their approach, though frequent splinter groups elect to go their own way.

In the long term the most significant difference of opinion in the socialist movement, in the years around the turn of the century, is between those who believe that socialism can be achieved in a gradual evolutionary process and, in opposition to them, the strict followers of Marx who insist that the prize must be won in a sudden and violent act of revolution.

From this split comes the eventual division of the socialist movement into two incompatible 20th-century branches: the social democrats who become a major force in western democracies; and the Communists, for more than half a century the only political party in the eastern bloc. The paths diverge first in Britain and in Russia.

The emergence of British socialism: 1881-1905

Britain acquires its own proto-Marxist party in 1881, when Henry Hyndman forms a Democratic Federation in London. In 1884 the group adopts a fully Marxist programme and changes its name to the Social Democratic Federation.

In that year, a significant one for British socialism, the new Federation suffers its first split when Engels encourages William Morris and others to break away and form an independent Socialist League. But far more important in the long run is a quite separate event of 1884. A group of intellectuals forms the Fabian Society, with the express purpose of working towards a democratic socialist state.

The Fabian Society's name indicates how far its intentions divert from Marx's policy of sudden revolution. It commemorates Fabius Cunctator, the Roman general who weakened Hannibal by a campaign of slow attrition. This approach is described in 1884 in one of the society's first pamphlets, entitled simply Manifesto and written by George Bernard Shaw. Other influential figures are the tireless left-wing couple Beatrice and Sidney Webb.

In 1889 the society publishes Fabian Essays in Socialism, edited by Shaw. Fabian policies by now influence many in left-wing British politics, including a trades union activist, James Keir Hardie, who has recently founded Britain's first labour party.

Hardie, who has gone down the mines in Lanarkshire at the age of ten, travels round Scotland from 1878 trying to organize a miners' union. In 1888 he founds the Scottish Labour Party. He has no electoral success in Scotland, but in 1892 he wins a seat in London as an independent Labour candidate.

In 1893 an Independent Labour Party is formed with Hardie as chairman. In 1900, at a congress of trades unions, this is expanded into a Labour Representation Committee. And in 1905, in preparation for a general election in 1906, the name is changed to the Labour Party. The party's candidates win twenty-nine seats. Labour is for the first time a democratic power to be reckoned with.

The electoral success in 1906 of the British Labour party is a significant step in the 20th-century split between Socialism (in the western sense) and Communism. Once it is evident that political progress can be made by these means, the socialist parties of the west commit themselves to parliamentary democracy and to a modified version of Marxist economics. They aim to nationalize the 'commanding heights' of the economy, but not to abolish private property in its entirety.

The fully Marxist programme achieves its first success in Russia, where in this same period of 1905-6 there is a dramatic outburst of revolutionary activity. But the roots of radical Russian politics go back much further.